I have read some of the recomendations given, and all are valid because there are so many reasons for which you could feel out of breath while swimming free style, especially begining a race in open water.
Ofcourse you must train correctly, style, drills, keep reading about it and tips, etc... Since you say swimming was never your thing... efficient swimming where you are relaxed and learn to glide with every stroke, breathe in a relaxed form, etc... is ussually found in swimmers that have learned and trained correct technique since childhood, like in many other sports. It will probably take longer for you to improve, but you must train adecuately, you were suggested some good drills of touching your hands together in front and rowing one arm at the time... also train slowly in the pool, breathing every 6 strokes, then every 8, etc... try to glide, you should have an experienced trainer to help you out to train according to your personal objectives.
Sometimes there are no shortcuts... you need time for adding and adding kilometers of swimming to your body thru time, and also experience in races, finding or discovering your mistakes, finding your pace, etc...
George